This invention relates generally to the testing of inflatable bags employed in the manufacture of fiber-reinforced plastic articles, such as tanks or the like, and more particularly to an apparatus and method for detecting and identifying the approximate location of defects in rubber stock which is to be formed into inflatable bags and used in the manufacture of such articles. In the manufacture of fiber-reinforced articles, randomly oriented fibers are formed in the approximate shape of the article to be molded and held in that shape by a resin binder. This preform, as it is called, is then encased within a rigid mold casing. An expandable bag, usually made from flat, thin rubber stock, which will define the interior shape of the finished article is placed within the laid up preform within the mold. The form is held in place in the mold by a suitably moderate pressure by inflating the bag with air to hold the fiber preform in place against the interior wall of the mold, and then the fiber preform is partially permeated with a thermosetting resin or the like. The bag is subsequently expanded by further inflation to compress the fiber form in such a manner as to distribute the resin throughout the fiber matting and achieve the results of pressure molding. The above-described process is set forth in U.S. Reissue Pat. No. 25,241 to Randolph.
It is essential that the expandable bag which is placed in the mold and inflated be absolutely airtight, since even a small pin hole-sized air leak will cause a structural defect in the wall of the finished fiber-reinforced article. Thus, it is desirable to detect and identify the location of air leak defects within the flat rubber stock used to manufacture the expandable bags. Once the defect is detected and located, that portion containing the defect can be cut from the rubber stock before it is used to manufacture the bags so that the resultant fiber-reinforced articles are free from structural defects caused by air leaks in the expandable bag.
In the past, detection of small air leak-causing defects in flat, thin rubber stock has been time-consuming and impractical. The disclosed invention solves these problems.